230V single phase motor running on 208V from 3 Phase System?

[jahilliard]

I have been asked to add a buck/boost transformer to help correct a voltage issue for a lake fountain motor. I have read this link http://forums.mikeholt.com/showthread.php?t=144958&page=3 and from what I gather is that if a transformer were to be added to adjust the voltage from 208V to 230V the transformer would need to be sized 3-5X larger to account for the inrush?? The actual information for this particular situation is a single phase 230V rated 3HP motor (lake fountain) is currently running on 208V from a 3 phase wye system. The distance from the source to the motor is approx. 250' and the actual voltage under load at the motor is 192V. The motor has quit working already after only running for about a month for approx. 8 hours a day. I haven't ever installed a buck/boost transformer and I am just searching to see if this is a practical fix or not...or should the fountain contractor just replace the motor with a 200v rated one...seeing as how it sounds like it may be toast already. FYI: There is a capacitor in the control panel I am assuming is to help compensate for some of the inrush on start up.

 

[jahilliard]

"As for the phase angle change through the transformers - that's a problem. One has to make sure the Sympathetic Inrush Harmonizers are adjusted correctly, or the inrush current can easily trip the feeder CB."
I am particularly wondering about this statement...anyone have any insight?

 

[jim dungar]

".... the Sympathetic Inrush Harmonizers are adjusted correctly, or the inrush current can easily trip the feeder CB."?

Where did you find this statement?:dunce:


A buck-boost transformer is very easy to implement in this situations. There is no inrush to speak of. You probably do not need to oversize for starting current. The hardest thing is to decide what voltage level you want for an output 229V or 236V.

 

[jahilliard]

ok.. ideally all I want to do is add the boost transformer to approx. 230V on the secondary. So if I were to simply add the transformer to the 208V and produce the approx. 230V and feed the 3hp motor everything should work as intended? When the control panel provides power to the transformer therefore turning the motor on.. there sould be no inrush on start up that would effect the transformer? Just making sure man...before I install this and more problems occur. BTW the statement is in the thread I posted a link to in the original post and there is also mention of the inrush and sizing a boost transformer to compensate for that.

 

[AdrianWint]

230V sounds like it might be a pump intended for a 50Hz European country......

Are you sure this device is suitable for 60Hz operation ?

(If it really is a 50Hz design its going to want to run faster on 60Hz ..........)

Adrian

 

[Jraef]

... FYI: There is a capacitor in the control panel I am assuming is to help compensate for some of the inrush on start up.

Not a safe assumption in my opinion. A capacitor in the control panel of a pump typically means one of two things:

1) The motor is actually a 3 phase motor, and the capacitor in the control panel is part of a "phase adder" system common to a lot of pump suppliers that import pumps from Europe. The Europeans use 3 phase in residences in many places, but over here we don't really have 3 phase available in residential installations. So the US distributors of these pumps sell them in a package that includes a "phase adder" system using a simple capacitor to get the motor started, then de-rate the pump because it is really running on single phase.

2) It is a submersible single phase pump, so the starting capacitor cannot be inside of the pump motor and it is put outside (in the control panel) then they will use a Potential Relay to switch the cap in and out instead of a centrifugal switch inside of the motor.​

So before you decide what you do, get to the bottom of why the capacitor is in the box, because if it is a phase adder from ASSUMING you have single phase, yet you really DO have 3 phase, then it makes a lot more sense to remove that and run the motor on 3 phase and it may be that you do not really need to boost the voltage. If it is just a starting cap for a true single phase submersible motor the problem might be related to the fact that your Potential Relay is not operating to remove the cap because it is set for a specific voltage that, because of the 208V supply and voltage drop, the relay never sees. That leaves the cap in the circuit too long, which can damage the cap and the motor. The transformer will be important, but it might be easier to just get a different Potential Relay.

 

[Besoeker]

Where did you find this statement?:dunce:

A poor translation in a document not originally written in English?

 

[Besoeker]

230V sounds like it might be a pump intended for a 50Hz European country......

Are you sure this device is suitable for 60Hz operation ?

(If it really is a 50Hz design its going to want to run faster on 60Hz ..........)

Adrian

Trust a Brit to come up with that daft idea!!

 

[Jraef]

230V sounds like it might be a pump intended for a 50Hz European country......

Are you sure this device is suitable for 60Hz operation ?

(If it really is a 50Hz design its going to want to run faster on 60Hz ..........)

Adrian

230V is the design voltage for motors expected to run on 240V systems here in the US.

 

[jahilliard]

The pump is a Franklin motor, 3Hp 230V single phase. I added the transformer to boost the voltage to 239V on the Load side of the starter leaving the Cap ahead assuming I just needed to boost the voltage going directly to the motor...yea that didn't work. I figured the Cap wasn't "sensing" what it should installed like that and I put the transformer ahead of everything and it seems to be working fine. The control circuits are separate from the Motor Voltage/circuit so they weren't effected by the "boosted" voltage.

 

[Jraef]

The pump is a Franklin motor, 3Hp 230V single phase. I added the transformer to boost the voltage to 239V on the Load side of the starter leaving the Cap ahead assuming I just needed to boost the voltage going directly to the motor...yea that didn't work. I figured the Cap wasn't "sensing" what it should installed like that and I put the transformer ahead of everything and it seems to be working fine. The control circuits are separate from the Motor Voltage/circuit so they weren't effected by the "boosted" voltage.

Yep, in a Franklin pump, that is the starting cap and there is a potential relay in there as well. So at the low voltage, that potential relay was not operating correctly.

 

[kwired]

Where did you find this statement?:dunce:


A buck-boost transformer is very easy to implement in this situations. There is no inrush to speak of. You probably do not need to oversize for starting current. The hardest thing is to decide what voltage level you want for an output 229V or 236V.

Keeping in mind that a buck/boost is not a solution for voltage drop. OP still may need to increase the conductor size to get a reliable installation.

If you install a BB to raise from 208 to 240 but are already seeing 192 volts when in operation, the BB is going to demand more current from the supply making the supply go even less then 192 when all is done. You only want to boost what you are short on not compromise for VD here - IOW the load is going to demand the same kVA regardless, but will make up for low voltage by drawing more current which will result in increased heating within the motor. The closer the motor is applied to it's full load rating the more it will effect it's ability to withstand this increased heating.

The pump is a Franklin motor, 3Hp 230V single phase. I added the transformer to boost the voltage to 239V on the Load side of the starter leaving the Cap ahead assuming I just needed to boost the voltage going directly to the motor...yea that didn't work. I figured the Cap wasn't "sensing" what it should installed like that and I put the transformer ahead of everything and it seems to be working fine. The control circuits are separate from the Motor Voltage/circuit so they weren't effected by the "boosted" voltage.

Good chance that capacitor is a start capacitor only connected to the starting winding portion of the motor circuit. You want the BB installed ahead of all motor components - which this capacitor is essentially a motor component.

Even if it were a phase conversion capacitor it is probably still best to have the BB ahead of it, if it is a power factor capacitor, it really doesn't matter where it is in relation to the BB, but PF correction is not something generally done on this small of a motor at the motor location. Small single phase motors often have a reasonably high power factor in the first place (AFAIK)

 

[broadgage]

IMHO, a buck/boost transformer CAN be used to at least partialy correct for voltage drop in the wires to the pump, but dont overdo it !
At present the 208 volt supply is dropping to 192 volts at the motor, or about 16 volts drop.

I would aim to boost the 208 volt supply not to 230 volts, but to a full 240 volts or a little more.

Boosting to only 230 volts at the transformer will give about 214 at the motor which might be marginal.
Boosting to 240 volts at the transformer would give about 225 at the motor which is better.
Boosting to 245 volts at the transformer would give about 230 volts at the motor which is probably optimum.

It would be unwise to go over 250 volts because when the pump stops there will be very little voltage drop and any controls etc will be overvolted.
250 volts actual is fine for 240 volt nominal controls etc as many 240 volt nominal services are nearer 250 actual.